1. Field of the Invention
The present invention relates to a refrigerant compressor, and more particularly, to a slant plate type compressor, such as a wobble plate type compressor with a variable displacement mechanism suitable for use in an automotive air conditioning system.
2. Description of the Prior Art
A wobble plate type refrigerant compressor with a variable displacement mechanism as illustrated in FIG. 1 is disclosed in U.S. Pat. No. 4,960,367 to Terauchi. For purposes of explanation only, the left side of the Figure will be referenced as the forward end or front end and the right side of the Figure will be referenced as the rearward end.
Compressor 10 includes cylindrical housing assembly 20 including cylinder block 21, front end plate 23 at one end of cylinder block 21, crank chamber 22 formed between cylinder block 21 and front end plate 23, and rear end plate 24 attached to the other end of cylinder block 21. Front end plate 23 is mounted on cylinder block 21 forward of crank chamber 22 by a plurality of bolts 101. Rear end plate 24 is mounted on cylinder block 21 at its opposite end by a plurality of bolts 102. Valve plate 25 is located between rear end plate 24 and cylinder block 21. Opening 231 is centrally formed in front end plate 23 for supporting drive shaft 26. Drive shaft 26 is supported by bearing 30 disposed in opening 231. The inner end portion of drive shaft 26 is rotatably supported by bearing 31 disposed within central bore 210 of cylinder block 21. Bore 210 extends to a rearward end surface of cylinder block 21 and has disposed within it valve control mechanism 19 which is discussed below.
Cam rotor 40 is fixed on drive shaft 26 by pin member 261 and rotates with drive shaft 26. Thrust needle bearing 32 is disposed between the inner end surface of front end plate 23 and the adjacent axial end surface of cam rotor 40. Cam rotor 40 includes arm 41 having pin member 42 extending therefrom. Slant plate 50 is adjacent cam rotor 40 and includes opening 53 through which passes drive shaft 26. Slant plate 50 includes arm 51 having slot 52. Cam rotor 40 and slant plate 50 are connected by pin member 42, which is inserted in slot 52 to create a hinged joint. Pin member 42 is slidable within slot 52 to allow adjustment of the angular position of slant plate 50 with respect to a plane perpendicular to the longitudinal axis of drive shaft 26.
Wobble plate 60 is rotatably mounted on slant plate 50 through bearings 61 and 62. Fork shaped slider 63 is attached to the outer peripheral end of wobble plate 60 and is slidably mounted on sliding rail 64. Sliding rail 64 is held between front end plate 23 and cylinder block 21. Fork shaped slider 63 prevents rotation of wobble plate 60 and, thus, wobble plate 60 nutates along rail 64 when cam rotor 40 rotates. Cylinder block 21 includes a plurality of peripherally located cylinder chambers 70 in which pistons 71 reciprocate. Each piston 71 is connected to wobble plate 60 by a corresponding connecting rod 72.
Rear end plate 24 includes peripherally located annular suction chamber 241 and centrally located discharge chamber 251. Valve plate 25 is located between cylinder block 21 and rear end plate 24 and includes a plurality of valved suction ports 242 linking suction chamber 241 with respective cylinders 70. Valve plate 25 also includes a plurality of valved discharge ports 252 linking discharge chamber 251 with respective cylinders 70. Suction ports 242 and discharge ports 252 are provided with suitable reed valves as described in U.S. Pat. No. 4,001,029 to Shimizu.
Suction chamber 241 includes inlet portion 241a which is connected to an evaporator of the external cooling circuit (not shown). Discharge chamber 251 is provided with outlet portion 251a which is connected to a condenser of the cooling circuit (not shown). Gaskets 27 and 28 are located between cylinder block 21 and the front surface of valve plate 25, and between the rear surface of valve plate 25 and rear end plate 24, respectively. Gaskets 27 and 28 seal the mating surfaces of cylinder block 21, valve plate 25 and rear end plate 24.
With further reference to FIG. 2, valve control mechanism 19 includes cup-shaped casing member 191 defining valve chamber 192 therewithin. O-ring 19a is disposed between an outer surface of casing member 191 and an inner surface of bore 210 to seal the mating surfaces of casing member 191 and cylinder block 21. A plurality of holes 19a are formed in the closed end (to the left in FIGS. 1 and 2) of casing member 191 to let crank chamber pressure into valve chamber 192 through a gap 31a existing between bearing 31 and cylinder block 21. Bellows 193 is disposed in valve chamber 192 to longitudinally contract and expand in response to crank chamber pressure. Projection member 193b is attached at a forward end of bellows 193 and is secured to axial projection 19c formed at a center of the closed end of casing member 191. Valve member 193a is attached at a rearward end of bellows 193.
Cylinder member 194, including valve seat 194a, penetrates a center of valve plate assembly 200. Valve plate assembly 200 includes valve plate 25, gaskets 27 and 28, suction reed valve 271 and discharge reed valve 281. Valve seat 194a is formed at a forward end of cylinder member 194 and is secured to an opened end of casing member 191. Nuts 100 are screwed on cylinder member 194 from a rearward end of cylinder member 194 located in discharge chamber 251 to fix cylinder member 194 to valve plate assembly 200 and valve retainer 253. Conical shaped opening 194b, which receives valve member 193a, is formed at valve seat 194a and is linked to cylindrical bore 194c axially formed in cylinder member 194. Consequently, annular ridge 194d is formed at a location which is the boundary between conical shaped opening 194b and cylindrical bore 194c. Actuating rod 195 is slidably disposed within cylindrical bore 194c, slightly projects from the rearward end of cylindrical bore 194c, and is linked to valve member 193a through bias spring 196. Bias spring 196 smoothly transmits the force from actuating rod 195 to valve member 193a of bellows 193. Actuating rod 195 includes annular flange 195a which is integral with and radially extends from an outer surface of a front end portion of actuating rod 195. Annular flange 195a is located in conical shaped opening 194b, and prevents excessive rearward movement of actuating rod 195 by coming into contact with annular ridge 194d. O-ring 197 is compressedly mounted about actuating rod 195 to seal the mating surfaces of cylindrical bore 194c and actuating rod 195, thereby preventing the intrusion of the refrigerant gas from discharge chamber 251 into conical shaped opening 194b via the gap created between cylindrical bore 194c and rod 195.
Radial hole 151 is formed at valve seat 194a to link conical shaped opening 194b to one end opening of conduit 152 formed in cylinder block 21. Conduit 152 includes cavity 152a and also is linked to suction chamber 242 through hole 153 formed in valve plate assembly 200. Passageway 150, which provides communication between crank chamber 22 and suction chamber 241, is formed by uniting gap 31a, bore 210, holes 19b, valve chamber 192, conical shaped opening 194b, radial hole 151, conduit 152 and hole 153.
As a result, the opening and closing of passageway 150 is controlled by the contracting and expanding of bellows 193 in response to crank chamber pressure.
During the operation of compressor 10, drive shaft 26 is rotated by the engine of the vehicle through electromagnetic clutch 300. Cam rotor 40 is rotated with drive shaft 26. Thus, slant plate 50 is also rotated, which causes wobble plate 60 to nutate. Nutational motion of wobble plate 60 reciprocates pistons 71 in their respective cylinders 70. As pistons 71 are reciprocated, refrigerant gas which is introduced into suction chamber 241 through inlet portion 241a, flows into each chamber 70 through suction ports 242 and is then compressed. The compressed refrigerant gas is discharged into discharge chamber 251 from each cylinder 70 through discharge ports 252, and therefrom flows into the cooling circuit through outlet portion 251a.
The capacity of compressor 10 is adjusted to maintain a constant pressure in suction chamber 241 in response to a change in the heat load on the evaporator or a change in the rotating speed of the compressor. The capacity of the compressor is adjusted by changing the angle of the slant plate which is dependent upon the pressure in the crank chamber relative to the pressure in the suction chamber. An increase in crank chamber pressure relative to the suction chamber pressure decreases the slant angle of the slant plate and the wobble plate, thus decreasing the capacity of the compressor. A decrease in the crank chamber pressure relative to the suction chamber pressure increases the angle of the slant plate and the wobble plate and, thus, increases the capacity of the compressor.
The purpose of valve control mechanism 19 of the prior art compressor is to maintain a constant pressure at the outlet of the evaporator during capacity control of the compressor. Valve control mechanism 19 operates in the following manner. Actuating rod 195 pushes valve member 193a in the direction to contract bellows 193 through bias spring 196. Actuating rod 195 is moved in response to receiving pressure in discharge chamber 251. Accordingly, increasing pressure in discharge chamber 251 further moves rod 195 toward bellows 193, thereby increasing the tendency of bellows 193 to contract. As a result, the compressor control point for displacement change is shifted to maintain a constant pressure at the evaporator outlet portion. That is, the valve control mechanism 19 makes use of the fact that the discharge pressure of the compressor is roughly directly proportional to the suction flow rate. Since actuating rod 195 moves in direct response to changes in discharge pressure and applies a force directly to the bellows 193 (the controlling valve element), the control point at which bellows 193 operates is shifted in a very direct and responsive manner by changes in discharge pressure.
In the construction of valve control mechanism 19 of the prior art compressor, O-ring 197 is compressedly mounted about actuating rod 195. Therefore, rod 195 frictionally slides through O-ring 197 in the operation of valve control mechanism 19. This causes the sliding movement of rod 195 within cylindrical bore 194c to be affected by frictional forces between O-ring 197 and rod 195, thereby producing a relationship between the suction chamber pressure and the discharge chamber pressure as illustrated in FIG. 8.
With reference to FIG. 8, line l.sub.0 shows the relationship between the suction chamber pressure and the discharge chamber pressure in an ideal condition (i.e., rod 195 slides within cylinder 194c with no sliding friction). Line l.sub.1 shows the relationship between the suction chamber pressure and the discharge chamber pressure in a discharge chamber pressure increasing stage. Line l.sub.2 shows the relationship between the suction chamber pressure and the discharge chamber pressure in a discharge chamber pressure decreasing stage. Line l.sub.1 is parallel to line l.sub.0 by the horizontal distance of .DELTA.P.sub.d1 along the abscissa, and line l.sub.2 is parallel to line l.sub.0 by the horizontal distance of .DELTA.P.sub.d2 along the abscissa. Distance .DELTA.P.sub.d1 is equal to distance .DELTA.P.sub.d2.
In the discharge chamber pressure increasing stage, the discharge chamber pressure will be increased from the discharge chamber pressure in the ideal condition by .DELTA.P.sub.d1 in order to compensate for the sliding friction force generated between rod 195 and O-ring 197. The increased increment .DELTA.P.sub.d1 is necessary to locate rod 195 in the same position that rod 195 would be in the ideal condition, to thereby obtain the same suction chamber pressure as in the ideal condition. In other words, in order to obtain suction chamber pressure P.sub.s0, the discharge chamber pressure is required to be P.sub.d1. However, in the ideal condition, discharge chamber pressure P.sub.d1 obtains suction chamber pressure P.sub.s1.
On the other hand, in the discharge chamber pressure decreasing stage, the discharge chamber pressure will be decreased from the discharge chamber pressure in the ideal condition by .DELTA.P.sub.d2 in order to compensate for the sliding friction force generated between rod 195 and O-ring 197. The decreased increment .DELTA.P.sub.d2 is necessary to locate rod 195 in the same position that rod 195 would be in the ideal condition, to thereby obtain the same suction chamber pressure as in the ideal condition. In other words, in order to obtain suction chamber pressure P.sub.s0, the discharge chamber pressure is required to be P.sub.d2. However, in the ideal condition, discharge chamber pressure P.sub.d2 obtains suction chamber pressure P.sub.s2.
As described above, in both the discharge chamber pressure increasing and decreasing stages, the suction chamber pressure in the ideal condition is obtained at a certain discharge chamber pressure, the value of which is different than the value of the discharge chamber pressure in the ideal condition. As a result, the valve control mechanism according to the prior art compressor does not compensate with as high a degree of sensitivity as it could for the increase in pressure at the evaporator outlet when the capacity of the compressor is adjusted, in order to maintain a constant evaporator outlet pressure.